ok i dont understand. by "range" im assuming NASA means the entire sky right? maybe a certain radius of it anyway? since the sky is all open and just "there" I dont get what this conflict is about? so what if numerous ships have a launch schedule close together, launch one, say at 10am, then launch another at 1030am---so what? why does the range only allow a certain vessel at a time to only launch at a certain period? the sky is the sky. Once something launches and clears, why cant another go right after it? even a day later, why is it still closed off?

"Range" is the Eastern Range formerly the Eastern Test Range which is managed by the 45th Space Wing. The "Range" include comm, telemetry, tracking, photo/video, range safety systems, weather forecasting systems, and security assets located on KSC, CCAFS, JDMTA, Antigua, and Ascension Island. The configuration of these assets is different for each launch vehicle type. For example, the launch trajectory information to allow for telemetry and tracking antenna pointing has to be distributed, loaded and verified. Same goes for the abort limits for range safety computers and displays. Comm channels have to be reconfigured, tracking camera moved and aligned. Road blocks moved and established. There is a finite amount of time required to do this work from one launch to another.

Could be because that gain would be smaller than increased gravity losses of a heavier orbiter earlier in the ascent.

Could be. But I doubt it. Do ~60kN (OMSs) out of ~6,000kN (SSMEs) really make such a difference with respect to gravity losses? I still think having to push a 30mt ET or not would be the bigger difference.

"OMS assist is performed if 1) the OMS prop required for the mission itself does not require full tanks and 2) the mission could benefit from the additional payload capacity gained by filling the OMS tanks full and burning the difference as OMS assist (IIRC it's roughly 200 lb payload for 4000 lb OMS prop). CG location is a secondary consideration on the amount"

Sorry if I steped on Jorge's answers earlier but they weren't visible when I typed mine.

As for RTHU, after STS-87 I think ALL flights performed the roll because it was implemented based on the performance enhancement certifications. Flight Procedures Handbook states it is REQUIRED for low inclination flights for that reason alone. FPH also states that roll costs about 35 lbs in performance.

I have the STS-97 checklist Jorge referred to in my files so I can look that up to confirm.

Mark Kirkman

This is what the STS-97 FLT cycle FOP minutes had to say about it:

Quote

The Program Office has recently approved a change in design to remove the Roll-to-Heads-Up from the ascent profile as a performance enhancement of ~50 to 100 lbs. The Flight Design community deems this change as undesirable to STS-97 because it requires a change to ascent design procedures and internal software verification tools before implementation. The time required to incorporate these changes may not be adequate to ensure all procedures and off-line software tools are implemented properly. However, ADFD management felt that the risk to implement the No RTHU on this flight was acceptable when weighted against the very low APM and future APM threats. The ADFD flight team will work to mitigate any risks due to this change by aggressively communicating details through the design community and carefully implementing any changes associated with a No RTHU maneuver. As a result, the SSP directed Flight Design not to perform the Roll-To-Heads-Up maneuver for STS-97 Flight Cycle in order to realize the APM gain. The STS-97 CDR asked if the Engineering Cycle load could be updated to include this change in training. This is being investigated and will be updated is possible.

So at one point no-RTHU was the baseline for STS-97. If STS-97 did fly RTHU, it must have been restored after the FLT cycle.

So at one point no-RTHU was the baseline for STS-97. If STS-97 did fly RTHU, it must have been restored after the FLT cycle.

FWIW, it's hardly definitive, but I don't hear any mention of a roll to heads up in the public broadcast of STS-97. On STS-98, Ken Cockrell added "and we're rollin'" when acknowledging the 'Press to MECO' call...

I guess what I'm wondering is what gives the greater benefit, loading those OMS tanks with fuel and then burning them, or not filling the amount that would be burned.

I assume from your answer that it's the former.

That is correct, and that is why OMS assist is done.

IIRC, the OMS tanks have to be filled completely (or as close to full as possible) because there is no sensor gage to tell you how much prop is in them. They have to fill OMS tanks completely to know with a high degree of certainty how much prop is in them at launch. Then, you burn what you don't need for the miss during ascent -- OMS assists -- and use calculations once on orbit to approximate how much OMS prop is left in the tanks after each firing of the OMS engines.

IIRC, the OMS tanks have to be filled completely (or as close to full as possible) because there is no sensor gage to tell you how much prop is in them. They have to fill OMS tanks completely to know with a high degree of certainty how much prop is in them at launch. Then, you burn what you don't need for the miss during ascent -- OMS assists -- and use calculations once on orbit to approximate how much OMS prop is left in the tanks after each firing of the OMS engines.

Am I remember incorrectly?

The OMS/RCS load may work this way, too, but you may be thinking of Steve Payne answering a question during a recent countdown briefing about PRSD offload and why it takes an extra shift or half-shift to do that. (His answer sounds similar to what you're describing.)

IIRC, the OMS tanks have to be filled completely (or as close to full as possible) because there is no sensor gage to tell you how much prop is in them. They have to fill OMS tanks completely to know with a high degree of certainty how much prop is in them at launch. Then, you burn what you don't need for the miss during ascent -- OMS assists -- and use calculations once on orbit to approximate how much OMS prop is left in the tanks after each firing of the OMS engines.

Am I remember incorrectly?

They do have level sensors in them but if they are used during fill i don't know.